With reference to FIG. 1, generators 1 have a casing 2 enclosing a stator 3 and a rotor 4 supported by a rotor shaft 5.
The rotor shaft 5 carries a fan 6 that, together with a fixed wall 7, having a hole in which the rotor shaft 5 is housed, defines a low pressure zone 8 (inside of the casing or being the outer environment) and a high pressure zone 9.
The stator 3 defines a plurality of stator phases each electrically connected to a phase ring 11 (FIG. 1 shows a traditional generator with three phase rings).
The phase rings 11 are electrically connected to bushings 12 through which the electric power generated by the generator 1 is transferred outside of the casing 2.
During operation the phase rings 11 and bushings 12 convey very high currents and thus must be cooled.
For this reason, the bushings 12 have an inner cooling circuit with an inlet that opens in the high pressure zone 9 to let a cooling medium 17 contained therein (for example the gas contained inside of the casing 2) enter, and an outlet that opens outside of the casing 2 and is connected to Teflon® pipes 14 that are connected to the low pressure zone 8 to discharge the cooling medium after it has cooled the bushings 12.
The phase rings 11 are hollow shaped with inlets that let the cooling medium contained inside of the high pressure zone 9 enter and pass through to cool them.
This traditional cooling system proved to be quite efficient, nevertheless new generators have been developing in which a plurality of phases (more then three) is connected to bushings (typically each phase is connected to two bushings).
It is clear that with these new generators it is very difficult and, for a very large number of phases (such as for example 15 or more phases), it could be practically impossible to implement a traditional cooling system.
In fact, since an increase of the number of phases also causes the number of bushings (being twice the number of phases) to be increased, no space may be available for the pipes 14.